HA-2m Sportster

[scandtours]

Wondering whether any HA-2m Sportster Gyroplane still flying.

I had the pleasure of flying one in Stockholm Sweden for many-many years ago.
Me first from the left.

 

[C. Beaty]

I remember Don Farrington relating his experience after going for a ride with Martin Hollmann in his “Sportster”at Rockford Illinois many years ago; “Two/rev vibration level was terrifying; I had already seen it fly the pattern so prayed that it would hold together for one more circuit.”
Rigid 2”x3” mast before it was widely understood that see-saw rotors required a compliant mount.

 

[Vance]

Martin Hollmann flat towed his gyroplane all over the country and flew it often for many years.

I will be flying a Hollmann Sportster phase one on my way to Mentone with a Lycoming O-320.

 

[C. Beaty]

According to Igor Bensen, Martin Hollmann’s problems came from living in the shadow of his father’s fame. The senior Hollmann, Hans Hollmann was an accomplished German physicist who contributed extensively to the development of radar in the years leading up to WW2.
The senior Hollmann was “recruited” by the US military at the end of WW2 and sent to live in California.
I became well acquainted with Martin during the time he worked for Martin Aircraft in Orlando and attended the U of Central Florida.. Martin dropped by my office whenever he was in Tampa and argued about rotors.

 

[scandtours]

I remember Don Farrington relating his experience after going for a ride with Martin Hollmann in his “Sportster”at Rockford Illinois many years ago; “Two/rev vibration level was terrifying; I had already seen it fly the pattern so prayed that it would hold together for one more circuit.”
Rigid 2”x3” mast before it was widely understood that see-saw rotors required a compliant mount.

As far as I remember all who had flown the Sportster experienced the same problem with stick shakes, C. Beaty.

 

[C. Beaty]

In an age before the internet, Arthur Young’s solutions for seesaw rotors were not well known.
Igor Bensen was one of the few, having worked at GE’s Schenectady research center on such things but even he settled for a square mast for the sake of expediency. Home builders with only an egg beater drill, a hacksaw and a file aren’t well equipped for working with round tube.
Bensen constantly reminded his customers not to do anything that would stiffen the mast such as adding external bracing.

 

[Doug Riley]

Igor's old Rotorcraft Dictionary reveals a little of his thinking. In the section about lag hinges, he says that the Gyrocopter achieves the same relief (that helos achieve with lag hinges) by using a flexible mast.

A bendy mast tube isn't a complete substitute for a Bell or Robbie mast suspension -- which is kind of a vertically-oriented version of a typical GA airplane engine mount, linking the bottom of the mast to the airframe. I guess that Martin, and many of us, wrongly believed that teeter-hinge undersling was enough by itself to eliminate 2/rev.

Then gyros got bigger, with the addition of second seats and massive 4-stroke engines, and we discovered we wuz wrong. Still, no gyro builder I know of uses a Bell-style mast suspension. Here's an image of the Robbie version. Four good old Barry mounts.

IMHO, anyone who copies this setup on a pusher gyro should NOT hang the engine or airframe off the middle of mast, Bensen-fashion. Run your structure around, and under the bottom of, the mast. Set your mast free!

 

[Brian Jackson]

Interesting discussion. Not to go too far off topic, but one of the things I'm hoping to address in my Gyrobee build is flexibility in the mast. The mast is folding, with the split point a few inches above the top of the diagonal seat braces. I'm aware that Sport Copter (and perhaps others) use an elastomeric bushing running crossways through the tube(s), which I envision serves the fore/aft movement, but I don't fully understand how this system would allow side-to-side flexibility. It seems the cheek plates would hinder that. Is there more going on with their folding mast system than I'm aware of? Thanks in advance.

 

[C. Beaty]

The primary flexibility requirement for a seesaw rotor is in the fore-aft direction. With the rotor broadside to the flight path, drag is higher than when end wise. It’s really no different than tossing a whirling broomstick.

 

[Brian Jackson]

The primary flexibility requirement for a seesaw rotor is in the fore-aft direction. With the rotor broadside to the flight path, drag is higher than when end wise. It’s really no different than tossing a whirling broomstick.

Thank you, Chuck. That does make perfect sense. I was under the impression that a round mast was preferred over square because it allowed some flexibility in all radial directions. If sideways movement (beyond normal, unbraced tube deflection) isn't needed then I'll not deviate from what's tried and true.

 

[Smack]

So, based on Chuck's fore/aft vibration note, a partial solution would be to turn that rectangular mast 90 degrees so the less rigid walls were fore/aft?

 

[C. Beaty]

While it is true that the major vibratory load input of a seesaw rotor in forward flight is in the fore/aft direction, I still prefer a small diameter round tube steel mast. Let it flex and absorb the vibratory input without rattling the airframe. Unfortunately, the real solution lies in a rotor with more than 2 blades. But then, we couldn’t pack a fleet of rotorcraft in a small hangar.

 

[C. Beaty]

Many years ago, at one of the earliest Bensen Days flyins, I rolled out my hingless, floating hub rotor; 3 blades with feathering bearings but no flap or drag hinges. The hub was a triangular aluminum plate with a blade/feathering bearing attached to each apex and with the hub attached to the rotorhead via a universal joint. There’s a video of it posted here somewhere.
As I taxied toward the start end of the runway for the first flight, Martin gathered up an audience and explained to them that it was going to fling itself asunder from not having flap hinges. As I came flying sedately past, one of Martin’s audience members said; “Turn around Martin and watch it flinging itself asunder.” That story was related to me by a member of Martin’s audience.
Birds, bugs and butterflys wings flap, rotor blades rotate. A rotorblade doesn’t actually flap about the ‘flap” hinge; the “flap” hinge is part of a universal joint that permits the blades to rotate about a different axis from the rotorhead axis. If the rotor’s hub is permitted to align itself with the rotor’s tip plane axis, individual flap hinges can be eliminated.

 

[Jean Claude]

Unfortunately, the real solution lies in a rotor with more than 2 blades...hingless, floating hub rotor; 3 blades with feathering bearings but no flap or drag hinges. The hub was a triangular aluminum plate with a blade/feathering bearing attached to each apex and with the hub attached to the rotorhead via a universal joint.

The control of the tips plane requires then an individual pitch of the blades, which is also a serious drawback.

 

[Doug Riley]

There are some other vibes tucked into a 2-blade rotor. The rotor's total thrust varies a little 2/rev; Bensen tossed out the figure of + 6 lb. for a B-8 size gyro.

Chuck, you brought up what Frank Robinson called "wee-waw," caused, IIR, by the difference in AOA in a coned rotor between the front and back blade when the rotor is at 12 o'clock - six o'clock.

Then there's the constantly varying angle of diagonal flow over the blades when they are at any position other than 3 o'clock - 9 o'clock.

Robinson seems to have known what he was doing. A well-maintained R-22 is way smooth.

 

[C. Beaty]

Ken Brock introduced me to Frank Robinson when I was on a business trip to the West Coast.The R-22 prototype was locate in a large and otherwise empty warehouse building.
I remember discussing pitch-flap and pitch cone coupling with him at the time. That’s when he came up with the term wee-waa.